Mass-Observation was a United Kingdom social research organisation founded in 1937. Their work ended in the mid 1950s but was revived in 1981. The Archive is housed at the University of Sussex.

Mass-Observation aimed to record everyday life in Britain through a panel of around 500 untrained volunteer observers who either maintained diaries or replied to open-ended questionnaires. They also paid investigators to record people's conversation and behaviour at work, on the street and at various public occasions including public meetings and sporting and religious events.

The early prime movers behind Mass Observation were anthropologist Tom Harrisson, poet Charles Madge and the film-maker Humphrey Jennings. Collaborators included the critic William Empson, the photographer Humphrey Spender, the collagist Julian Trevelyan, and the painters William Coldstream and Graham Bell.

They developed a large number of techniques that laid the foundations of market research

The original phase ended after criticism from academics that such subjective work lacked validity. Changes in attitudes led to its relaunch in 1981. Today Mass-Observation continues to collect the thoughts of its panel of writers through regular questionnaires (known as directives) and is used by students, academics, media researchers and the public for its unique collection of material on everyday life in Britain.